1. Field of the Invention
The present invention relates generally to adhesives, used for joining ABS (acrylonitrile-butadiene-styrene) molded and extruded items. Specifically, the ABS adhesives disclosed and claimed herein are solvent-based, having an environmentally-acceptable VOC (volatile organic compounds) content.
2. The State-of-the-Art
Solvent-based adhesives have been in use for joining thermoplastic pipe for over 30 years. The development of these adhesives is largely responsible for growth of the thermoplastic pipe industry. Several billion pounds of plastic pipe are produced each year in North America. Rapid-setting, solvent-based adhesives weld the pipes together in a timely manner. These rapid-setting adhesives allow for the testing and trouble-shooting of piping systems in a matter of hours while maintaining the long-term durability of the pipe itself. These characteristics, rapid set, ease of use, long-term durability along with low-cost, have made the joining of plastic pipe by solvent-based adhesives a practical and economic system.
The solvent-based adhesives work primarily by two means of action. First, the solvent portion of the formulation softens the outer surfaces of the pipe through solvation of the plastic. Subsequently, the adhesive joint `cures` (hardens) by means of the solvents evaporating to the surrounding atmosphere from the pipe. Secondly, the resin dissolved in the adhesive dries through solvent evaporation and provides continuity between the welded pipe surfaces which aid in preserving the integrity of the entire pipe system.
These adhesives cure rapidly (within a matter of hours), often allowing piping systems to be tested the same day as constructed. However, perhaps the most important benefit of these solvent-based adhesives is the maintenance of the integrity of the pipe itself. The resin is the same as the plastic pipe. This provides a high degree of long-term durability for the piping system, often up to 30 to 40 years of useful life. This is essential for these systems which are built into the structures of homes and buildings, or are buried underground.
Thousands of miles of thermoplastic piping systems are constructed each day throughout the world, primarily by the means previously described. These systems are predominately used in non- or low-pressure systems, such as drain, waste, and vent (DWV) applications in home and industry, gas conduit, sewer applications, etc.
Evaporation of solvents from adhesives is a concern to an environmentally-concerned world, along with all other potential sources of air pollution. Typical solids (non-volatile) contents of plastic pipe adhesives are 15 to 30 wt % of ABS resin, or compound. The balance of the formulation is methyl ethyl ketone (MEK) solvent, as specified by ASTM D-2235. By definition, MEK is considered to be a VOC. That is, MEK is a volatile compound which contains the element carbon excluding methane, carbon monoxide, carbon dioxide, carbonic acid, metallic carbides and carbonates, ammonium carbonate, and exempt compounds, such as methylene chloride and 1,1,1-trichloroethane. Typical VOC values of present commercial ABS solvent adhesives range from 650 to 750 grams/liter.
Regulations are being created throughout North America regarding allowable VOC levels in adhesive formulations. Federal, state, and local agencies are beginning to adopt strict measures to drastically reduce these levels. The south Coast Air Quality Management District (SCAQMD) in the Los Angeles area has been a leader of the establishment of rules governing VOCs, such as SCAQMD Rule 1168.
SCAQMD Rule 1168 specifies a VOC level for ABS adhesives of 350 g/l or less, as determined by Method 316-A. All ABS adhesives used after Jan. 1, 1994, are required to meet that maximum allowed level.
Thus, an ABS adhesive for joining ABS molded and extruded items, such as pipes, having a maximum VOC level of 350 g/l is required.